Adhesives with high bonding and holding performance, which are detachable without residue from a bonding substrate by means of extensive stretching, are known. Adhesives for this purpose may be formulated advantageously on the basis of vinylaromatic block copolymers and tackifier resins.
The diverse applications of adhesive strips featuring such adhesives include bonds to walls, and more specifically not only to smooth, planar substrates, but in particular also to any rougher surfaces such as plaster, wood, woodchip wallpaper, especially coated woodchip wallpaper, other textured wallpapers, panels, or wall boards. Here as well there is a desire to affix articles, even those of high weight, without damaging the substrate (the wall). In the case of adhesive bonding, to coated woodchip wallpaper, for example, there are three particular challenges which arise, however, by comparison with numerous other substrates: (a) woodchip wallpaper is not a smooth bonding substrate; (b) the surface of the woodchip wallpaper typically carries a paint, which because of binders and/or additives may have a low surface energy; (c) woodchip wallpaper in particular constitutes a relatively easily splittable bonding substrate, which is not to be damaged during redetachment. The surface properties may vary greatly according to the nature of the paint. A further aspect is the moisture content of the coated woodchip wallpaper, which is dependent on the time of day, the season, and the geographical region, and which accordingly may also be subject to temporary fluctuations. For others in the list of example substrates given above, all or some of these challenges are applicable similarly. For these purposes, suitable adhesives are required. Also required are adhesive strips featuring adhesives with high bonding and holding performance which can be detached without residue and as far as possible without destruction from coated plaster or other rough surfaces, by extensive stretching.
Pressure-sensitive adhesive strips which have a high elastic or plastic extensibility and which are redetachable without residue or destruction by extensive stretching in the bond plane are known from, for example, U.S. Pat. No. 4,024,312 A, DE 33 31 016 C2, WO 92/01132 A1, WO 92/11333 A1, DE 42 22 849 A1, WO 95/06691 A1, DE 195 31 696 A1, DE 197 08 366 A1, DE 196 49 727 A1, DE 196 49 728 A1, DE 196 49 729 A1, DE 197 08 364 A1, DE 197 20 145 A1, DE 198 20 854 A1, and DE 100 03 318 A1, and below are also referred to as strippable pressure-sensitive adhesive strips or simply as (adhesive) strips. For these adhesive products it is possible with particular advantage to use formulations comprising styrene block copolymer.
The application of bonding adhesive strips to woodchip wallpaper has likewise been described before in principle, and is a typical application in the household and in offices.
DE 10 2004 030 252 A1 describes a hook system to be affixed to a rough substrate, this system allowing the adhesive strip to be detached nondestructively from the sensitive surface. Specific embodiments of the adhesive of the adhesive strip redetachable by extensive stretching are not given.
EP 845 513, EP 845 514, and EP 878 526 describe requirements associated with bonding to rough substrates, and observe that high bond strengths can in general be achieved on smooth and firm substrates using the self-adhesive tapes identified before. On rough substrates, there are numerous applications for which the bond strength is inadequate, especially for products of low thickness, but also for self-adhesive tapes of relatively high layer thickness. The cause of the inadequate bond strength is assumed to be an insufficient bond area, owing to inadequate conformability of the adhesive tapes to rough and irregular surfaces. As a solution, EP 845 513 A2 proposes the use of specific foam carriers in the adhesive products. Pressure-sensitive adhesives employed are preferably those based on block copolymers containing polymer blocks formed from vinylaromatics, preferably styrene, and blocks formed by polymerization of 1,3-dienes, preferably butadiene and isoprene. Block copolymers of these kinds can be used with a variety of architectures, and hence diblock copolymers may also be present. Typical concentrations in which the styrene block copolymers are used are located in the range between 15 wt % and 75 wt %, preferably in the range between 30 wt % and 60 wt %, more preferably in the range between 35 wt % and 55 wt %. Nothing is said about the fraction of diblock copolymers in relation to the total block copolymer content. One exemplary adhesive is composed of a mixture of a polystyrene-polybutadiene block copolymer (Vector 8505), a polystyrene-polyisoprene block copolymer (Vector 4211), and an ester of a partially hydrogenated rosin as tackifier resin. These block copolymers contain substantially no diblock copolymers.
U.S. Pat. No. 6,231,962 B1 and U.S. Pat. No. 6,403,206 B1 likewise describe double-sided adhesive strips featuring a foam carrier. Bonding substrates indicated for bonding applications are sensitive, easily splittable substrates such as painted wall panels, but not particularly rough substrates such as coated woodchip wallpaper. The adhesive used may comprise formulations based on styrene block copolymer. In specific example formulations, mineral oil is utilized to be as plasticizer. This is a disadvantage in the context of application to woodchip wallpaper, since the substrate may become saturated with grease, and this saturation may remain visible after removal of the adhesive strip.
EP 1 988 144 A1 proposes adhesives which in relation to the total resin amount contain at least 40% of a plasticizing resin. Stated applications include the bonding of lightweight (papers) to moderately heavy objects to woodchip wallpaper. The objective of such formulations is not that of high holding power, but instead the possibility of parting the bond, even from woodchip wallpaper, by extensive stretching or peeling. The diblock content of the elastomers is not specifically claimed. The examples describe formulations which have a diblock content either of >45% (example 1) or of <30% (examples 2-4).
U.S. Pat. No. 7,276,272 B2 describes double-sided adhesive strips which are redetachable even from sensitive substrates such as plaster, paint, or wallpaper. No bonding substrates featuring particularly pronounced roughness are indicated. For adhesives, moreover, reference is made merely to earlier general texts relating to strippable adhesive products (U.S. Pat. No. 4,024,312, U.S. Pat. No. 5,516,581, U.S. Pat. No. 6,231,962, and DE 33 31 016) WO 2002/038692 A2 describes adhesive products which are redetachable without residue or destruction by extensive stretching in the bond plane and which feature an adhesive based on styrene block copolymers with specific aging inhibitors that exhibit reduced propensity for discoloration on the bonding substrate. For these products, bonding to coated woodchip wallpaper, for example, is described. The text does not disclose any polystyrene-polybutadiene block copolymer-containing adhesives with a specific ratio of triblock copolymer to diblock copolymer.
DE 10 2007 063 083 A1 describes styrene block copolymer-based adhesives for nonpolar substrates. For this purpose, the adhesives described therein are admixed with a high fraction of a plasticizing resin. The amount claimed is at least 30%, based on the total resin amount. Moreover, the adhesive comprises at least two block copolymers, of which the first is a diblock copolymer and the second may be a multiblock copolymer, in the simplest case a triblock copolymer. The diblock fraction, relative to the total block copolymer content, is at least 50%. Adhesive products based on such adhesives and redetachable without residue or destruction by extensive stretching in the bond plane are not specified in the text, and nor is the use on rough substrates.
WO 2000/024840 A1 describes styrene block copolymer-based adhesives for nonpolar substrates. The adhesive comprises at least two block copolymers, of which the first is a diblock copolymer and the second may be a multiblock copolymer, in the simplest case a triblock copolymer. The diblock fraction, relative to the total block copolymer content, is at least 40% and at most 95%. Bonding to rough substrates, and adhesive products which are redetachable without residue or destruction by extensive stretching in the bond plane, are not specified. Formulations that are explicitly specified always contain mineral oil, leading to the risk of grease saturation on woodchip wallpaper.
DE 10 2013 2106 624 A1 describes adhesive products which are redetachable without residue or destruction by extensive stretching in the bond plane and which feature an adhesive based on styrene block copolymers, particular features being transparency and ozone stability. It is possible to utilize mixtures of triblock copolymers and diblock copolymers. The diblock copolymer fraction in the total block copolymer content is at most 50%. Tip-shear loading on woodchip wallpaper is not mentioned. Explicit examples have a diblock content of <30%.
DE 10 2008 023 741 teaches pressure-sensitive adhesives containing styrene block copolymer, with a total block copolymer content of at least 50%, for bonding printing plates.
Applications on woodchip wallpaper, and redetachability performed by extensive stretching, are not mentioned. Examples with polystyrene-butadiene block copolymers contain 60% of elastomer, based on the adhesive.
There continues to be a demand for adhesives which, for self-adhesive strips redetachable by extensive stretching, are especially suitable for rough substrates, particularly on coated woodchip wallpaper.
The desire is therefore for pressure-sensitive adhesives for self-adhesive strips redetachable by extensive stretching, more particularly for bonding to splittable and/or rough and/or coated substrates, with high bonding and holding performance.